September 26, 2018

Introduction

Introduction: Waders in the Wadden Sea

Waders such as red knots Calidris canutus gather in large non-breeding flocks in the Wadden Sea, where they forage on the intertidal mudflats

Wadden Sea mudflats

Wadden Sea mudflats

Knots benefit from sociality

Knots can use social information in lab settings to find food[1], and may learn the location of profitable foraging patches by observing flock-mates[2]

1: Bijleveld et al. 2015. Behav. Processes 2: Bijleveld et al. 2010. Oikos

Do knots have friends?

Knots benefit from association, but do they have friends — persistent, non-random associations — within & between tidal intervals[3][4]?

3: Myers 1983. Behav. Ecol. Sociobiol. 4: Conklin & Colwell 2007. J. Field. Ornith.

Methods: Tracking multitudes

ATLAS tracking

We set up ATLAS — a tracking tower system (n = 5) based on the Time of Arrival (ToA) of radio signals from tagged knots (n = 35)

Tracking tower and locations

Tracking tower and locations

Tidal intervals

  • We obtained water-level data from Harlingen

  • Identified 44 tidal intervals (~12 hrs) over 19 calendar days

  • Grouped each knot's movement tracks by tidal interval

Co-occurrence

  • Calculated co-occurrence cij

  • cij = proportion of positions at which birds i & j were within 250 m of each other

Results: Knot association is low

Most knots rarely interact

Pair-wise co-occurrence distribution

Pair-wise co-occurrence distribution

Knot co-occurrence is rarely different from random

Pair-wise co-occurrence matrix

Pair-wise co-occurrence matrix

Only ~10% of knot pairs are 'friends'

% of pairs with _c<sub>ij</sub>_ values higher than expected

% of pairs with cij values higher than expected

Results: Knot association is environmentally driven

Knot co-occurrence is tidally forced

Post foraging co-occurrence is unrelated to pre-foraging scores

  • GLMM: post-foraging cij ~ pre-foraging cij + foraging period distance mismatch + (1|pair) + (1|tidal interval)

  • Pre-foraging cij is not a significant effect (z = 1.738, p-value = 0.08)

  • Knots don't re-unite with pre-foraging 'friends'

Post-foraging co-occurrence is related to distance mismatch

  • Knots which travel similar distances during foraging are more closely associated post-foraging (z = -2.72, p-value = 0.006)

Discussion

At what scales do interactions happen?

  • Wader interactions may occur at scales not measured here

  • Knots have previously been shown to be non-randomly associated[5]

5: Harrington & Leddy 1982. Wader Study Group Bull.

Neighbour type might matter more than identity: Future work

  • Knots have consistent personalities re: exploratory behaviour[6]

  • May associate with individuals of similar personality due to shared resource requirements

  • Identification of neighbour personality may still require sustained association

6: Bijleveld et al. 2014. Proc. Royal Soc. B

Thank you!